Quote Originally Posted by ericgrau View Post
CO is created simply from combustion in the presence of insufficient oxygen (such as an enclosed space). It weighs about the same as air; it isn't really lighter or heavier. CO2 is heavier than air. Death by either is essentially death by suffocation. But if that were the issue I think we'd see a lot of smoke as well.

CO2 is death by suffocation, there's insufficient oxygen to allow for passive transport. CO is worse, it preferably binds to hemoglobin, meaning your red blood cells prefer to carry it over oxygen, and won't let it go.